Various methods have been devised and demonstrated for forming partial films on a transparent sheet or plate made of glass or plastic, thereby defining portions through which light rays are transmitted and the other portions which inhibit the transmission of the light rays. In order to define the light-transmission portions and the non-light-transmission portions which are spaced apart from each other by a very small distance, it is useful to employ a photoetching process which is used to fabricate integrated circuits and so on.
According to the photoetching process, a plurality of precision photomasks must be used and registered with each other with an extremely high degree of accuracy.
However, it is very troublesome to define lighttransmission portions and non-light-transmission portions which are spaced apart from each other by a very small distance on glass or plastic three-dimensional bodies with uneven surfaces such as compound lenses, compound prisms, Fresnel lenses or lenticular plates (corrugated lenses) for forming three-dimensional photos, and glass or plastic Fresnel sheets or plates by such photoetching process. Furthermore, their considerably high coefficients of thermal expansion must be taken into consideration, so that the film coating process including the temperature control system becomes very complicated. As a result, they are not suited to be mass produced, whereby their costs become very high.
The present invention was made to overcome the above and other problems encountered when specified portions of an uneven surface of an object are coated with films and the object of the invention is to provide a method for forming partial films over an uneven surface of an object in which the uneven surface of the object, especially an optical-path-varying object such as a lens, prism, Fresnel plate or the like is irradiated with parallel, converged or diffused light rays coming from a specific direction and thereafter the uneven surface thus exposed to the light rays is subjected to etching and washing steps so that colored films (for instance, black films) are formed at specified portions of the uneven surface of the object which are spaced apart from each other by an extremely small distance, in a positive manner and at less cost without the use of photomasks, temperature controls, and precision steps which are required in the conventional methods.